A conventional network analyzer displays the scattering parameters, or S parameters, S.sub.11 and/or S.sub.22 of a device under test (DUT) on a Smith chart. (S parameters are reflection and transmission coefficients and are familiar to RF and microwave designers. S parameters are directly related to impedances and reflection coefficients.) The user then determines the necessary characteristics of a matching circuit by reading the information displayed on the Smith chart. The matching circuit's purpose is to improve the reflection coefficient of the DUT, i.e., to match the impedance of the DUT to the characteristic impedance of its intended environment. The user graphically designs the matching circuit by plotting the DUT's S parameters on a Smith chart and determining the complex impedance and/or admittance values necessary to transform the S parameters to a prescribed point or set of points on the chart. However, it is often very difficult to accurately read data from the Smith chart.
Alternatively, one could have a computer such as an EWS (engineering workstation) acquire the measurement data and calculate the desired matching circuit data with CAE (computer aided engineering) software. This method, however, requires software for controlling a measuring instrument (e.g., a network analyzer) and for data transmission in addition to the computer and CAE software, rendering the system unnecessarily large and expensive.
Moreover, the method of programming an EWS or the like to acquire the measurement data from a network analyzer and carry out the necessary calculations is not suitable for performing real-time evaluations that follow changes in the environment (e.g., changes in temperature) of the DUT.
Furthermore, in many cases the calculated values of the parameters of the matching circuit do not coincide with those of realizable circuit elements (such as inductances and capacitances). Accordingly, it may be necessary to evaluate the characteristics of the DUT with an actual matching circuit attached.
In addition, if the user has only a network analyzer, he or she must actually make a trial matching circuit and measure its characteristics.